On Mon, Aug 16, 2021 at 10:38:56AM -0400, Alan Stern wrote:
> On Mon, Aug 16, 2021 at 04:13:47PM +0200, Michal Kubecek wrote:
> > Looking at the code, the primary problem seems to be that the "else"
> > branch in hid_submit_ctrl() recalculates transfer_buffer_length to
> > a rounded up value but assigns the original length to wLength.
> 
> Looks like you found the bug.  Fixing it might be as simple as setting 
> len = padlen in that "else" branch.  You could then combine the 
> transfer_buffer_length assignment with the one in the "if" branch and 
> hoist them out after the entire "if" statement.

With the patch below, there are no errors and the UPS communication
works correctly and so do other HID devices. But I would prefere someone
familiar with HID code to confirm that this is what we want and what
would be the right way to handle usb_submit_urb() errors.

Michal

diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index 06130dc431a0..ef240ef63a66 100644
--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -377,27 +377,26 @@ static int hid_submit_ctrl(struct hid_device *hid)
 	len = hid_report_len(report);
 	if (dir == USB_DIR_OUT) {
 		usbhid->urbctrl->pipe = usb_sndctrlpipe(hid_to_usb_dev(hid), 0);
-		usbhid->urbctrl->transfer_buffer_length = len;
 		if (raw_report) {
 			memcpy(usbhid->ctrlbuf, raw_report, len);
 			kfree(raw_report);
 			usbhid->ctrl[usbhid->ctrltail].raw_report = NULL;
 		}
 	} else {
-		int maxpacket, padlen;
+		int maxpacket;
 
 		usbhid->urbctrl->pipe = usb_rcvctrlpipe(hid_to_usb_dev(hid), 0);
 		maxpacket = usb_maxpacket(hid_to_usb_dev(hid),
 					  usbhid->urbctrl->pipe, 0);
 		if (maxpacket > 0) {
-			padlen = DIV_ROUND_UP(len, maxpacket);
-			padlen *= maxpacket;
-			if (padlen > usbhid->bufsize)
-				padlen = usbhid->bufsize;
+			len = DIV_ROUND_UP(len, maxpacket);
+			len *= maxpacket;
+			if (len > usbhid->bufsize)
+				len = usbhid->bufsize;
 		} else
-			padlen = 0;
-		usbhid->urbctrl->transfer_buffer_length = padlen;
+			len = 0;
 	}
+	usbhid->urbctrl->transfer_buffer_length = len;
 	usbhid->urbctrl->dev = hid_to_usb_dev(hid);
 
 	usbhid->cr->bRequestType = USB_TYPE_CLASS | USB_RECIP_INTERFACE | dir;